There are no straight external walls on the new V&A Dundee. Hence the challenge of designing, manufacturing and installing the 2,400 precast concrete panels that bring this geometrically complex design to life. But how did the use of Tekla’s BIM software help to make it happen?
This project reference explores what the design challenges on this intricate building were and how Tekla software aided architectural precast cladding specialist Techrete as well as the wider schedule of work.
When speaking to Sean Twomey, Drawing Office Manager at Techrete, about this exceptional project, he said straight away:
Hand on heart, the precast element of V&A Dundee could not have been done in 2D.
Sean Twomey, Drawing Office Manager at Techrete
The first V&A museum outside of London, V&A Dundee sits on the banks of the River Tay and forms the anchor to the transformation of the city’s waterfront. The impressive three-storey, 8,000m² building stands 18.4m high and offers 1,650m² of gallery space.
Vision of architect Kengo Kuma, the building’s extraordinary form is inspired by the nearby coastal cliffs. Partly constructed on reclaimed land, the site was excavated to 6.5m and, with 11m-deep piles, a massive cofferdam was created to give the appearance of the building sitting over the river.
Sloping inwards and outwards, the twisting concrete walls hold 2,400 precast rough stone panels, which form V&A Dundee’s façade. They weigh up to 3 tonnes each and span up to 4m long. BIM was used throughout. Every single precast plank was modelled by Techrete. This allowed the design team to search the model, zoom in and spin the plank around to check it fitted the design.
The real-life benefits of working this way
To realise the complicated shapes and geometry involved, Techrete chose to model the project in 3D using Tekla Structures, Dave McDonnell, Lead Project Modeller, explains: “Trimble’s Tekla Structures is intelligent software that suits our manufacturing process; it works with both steel and concrete.
It allows clash detection, gives weights and the centre of gravity of elements and, generates the fabrication drawings and rebar cutting schedules. This minimise errors, conflicting detailing documents and inefficient information transfer, which can waste material and resources and cause costly rework in the detailing department, factory and on site.
The architect supplied a 3D model, plans and schedules. From these, Tekla Structures was able to calculate and generate the setting out of the planks and fixings, the main contractor’s work and fabrication drawings, bracket details and schedules.
Three top widths of planks were proposed, 50, 150 and 250 and because of the acute reverse slope, a fourth 350-size panel was introduced. The top and bottom of the planks were positioned 130mm off the wall.
When looking along any of the elevations, each bracket and plank twists to follow the in situ walls whilst at the same time keeping the support point level, so the panels follow a horizontal line.
Because of the twisted walls and rotating geometry, different brackets and cast in hooks had to be used for different locations, Dave McDonnell explains how this was achieved:
We used Tekla Open API to customise the functionality of Tekla Structures to suit with our own software. This meant the programme could pick the correct brackets and fixings for each location. It also scheduled the components for ordering.
Opting for a construction system that allowed for the brackets to be set out accurately on the structure, the brackets were bolted into stainless steel channels previously cast into the structure. Tekla had generated an IFC file of the model for the in situ concrete subcontractor so that these channels could be located and cast in.
We designed the brackets with a vertical and horizontal tolerance so that they could be accurately positioned, which proved to be very successful. With the bracket precisely located on the structure, the panels only had to be hooked on and the lock-in bolts inserted.
To emulate the appearance of a cliff elevation, the concrete chosen for this project was made with grey granite aggregate and sand. The finish is an exposed aggregate achieved by retarding the cement paste to expose the underlying aggregate. Given the museum’s marine location, it was decided to use high-grade duplex 1.4662 stainless steel fixings which had additional surface finishes to enhance corrosion protection. These fixings were physically load tested to ensure that they met the structural requirements.
Twisted walls and rotating geometry - the model output assists at every step
To manufacture the 2,400 precast planks, output from the Tekla model provided the necessary information to design the moulds and fabricate them into, what Techrete termed, family groups to accommodate each of the plank widths.
With the planks twisting in section, the moulds were fabricated so that they rotated allowing for the top surface of the casting to be level or almost level. As part of the mould system, a sliding channel and retaining bracket were incorporated to locate the cast in hooks accurately within the precast planks.
The manufacturing period, which occupied approximately 15% of Techrete’s production capacity, commenced in August 2016 and lasted for a year. The precast specialist also carried out two months of on-site preparatory works, to ensure the 8,787m of planks could be installed smoothly. On a day-to-day basis the cloud-based Tekla Model Sharing collaboration tool facilitated this process, allowing teams to work on the same model at the same time, without their work colliding.
With 21 walls and up to 30 plank levels with very little repetition, it was very important to ensure that the manufactured planks were loaded onto the trucks and arrived on site in the defined construction order.
Using Tekla Structures, each plank was given a unique reference number, which designated the wall it was on, the level it was at and its position along the row. This also enabled a detailed tracking system from manufacture to final construction, helping to monitor the process and ensure its progress according to the schedule. The erection of the precast planks on site posed some interesting challenges, taking into consideration the fact that they weighed up to 3 tonnes each and had to be positioned up to 19m above ground level.
Again using the Tekla model, the Techrete team worked with the object data and location information to assist with the design and construction of specialist lifting equipment to ensure the safe and accurate placement of the planks on the building, accounting for the complex geometry of the walls.
At vertical and back-sloping walls, mobile cranes were employed. At overhanging walls at a low level, teleporters with specially modified attachments that allowed for fine adjustment were used. At higher levels above the reach of the teleporter, balanced lifting beams were able to reach in under the structure to erect the panels. At times, 22 planks were being installed each day.
Thanks to the BIM modelling, the fixing system design, and the efficient delivery and erection processes employed, the installation of all the planks was completed 12 weeks ahead of programme.
Images courtesy of Techrete, Ross Fraser McLean & Hufton + Crow Photography